Top 50+ Node.js Interview Questions and Answers for 2023

Node.js is a server-side platform that is being used by many organizations. It is always a great idea to go fully prepared with every topic for the interview. in interview, many candidates are asked questions about node.js so to avoid such a situation and not put yourself in a bad impression, it is always better to go through some of the questions about Node.js We have discussed below various questions related to Node.js from beginner level to the advanced level.

Q1. Define Node.js and Where to use it?

Node.js can be defined as an open-source, cross-platform JavaScript library to run that is used for web applications outside the client’s browser. As it uses a model that is synchronous and event-driven which makes it ideal for data-intensive applications. It is used to develop server-side web applications.

Q2. Why do we need Node.js?

Node.js makes it easy to build scalable programs. Some of the benefits of Node.js are:

  • It is fast.
  • Rarely blocks.
  • It provides a unified programming language and data type.
  • Totally asynchronous.
  • It provides great concurrency.

Q3. Explain the working of Node.js?

Below are the steps that define the workflow of Node.js

  • Clients send requests to the webserver to interact with the web application. Requests can be of two types non-blocking or blocking:
  • Querying for data
  • Deleting data
  • Updating the data
  • js receives the incoming requests and adds those to the Event Queue
  • The requests are then passed one by one through the Event Loop. It checks whether requests are simple, if yes then they do not to require any external resources
  • The Event Loop processes simple requests that are non-blocking operations, like I/O Polling, and returns the responses to the corresponding clients.

Q4. Tell a reason why Node.js is single-threaded?

Node.js is single-threaded for async processing as it helps in achieving

More performance and scalability.

Q5. How does Node.js handle concurrency in spite of being single-threaded?

Node.js does not follow the multithreaded request model. The Node.js processing involves a heavy JavaScript event model due to which it can easily handle more concurrent client requests. The event loop plays a very important role in Node.js.

Q6.  What is call back in Node.js?

After a given task, a call-back function is called. In the meantime, it allows the code to run and prevents any blocking. As Node.js is an asynchronous platform, it completely relies on the call-back function.

Q7. How are promises advantageous over callbacks?

  • Asynchronous logic control flow is structured and specified.
  • Low coupling.
  • Built-in error handling.
  • Readability is better.

Q8. What is the I/O term?

The term I/O is referred to any program, operation, or device that is used to transfer data to or from one medium to another.

Q9. What is the application of Node.js?

Node.js has the following application:

  • Real-time chats.
  • Complex SPAs (Single-Page Applications).
  • Real-time collaboration tools.
  • Streaming applications.
  • Microservices architecture.

Q10. Differentiate between front end and backend?

Front End:

  • It refers to the client-side of an application.
  • Users can see and interact with it as it is part of a web application.
  • Some of the essentials of frontend development include HTML, CSS, JavaScript, AngularJS, and ReactJS.

Back End:

  • It refers to the server-side of an application.
  • It constitutes everything that happens behind the scenes.
  • Some of the backend developments are ava, PHP, Python, and Node.js.

Q11. Define NPM?

NPM stands for Node Package Manager and is used to manage the packages and modules for Node.js.

The main functions of NPM are:

  • It gives online repositories for node.js packages/modules, that can be searched on
  • To install Node.js packages it used a command-line utility and also manages Node.js versions and dependencies.

Q12.  List Modules in Node.js?

To include a set of functions in Node.js modules are used that act as libraries.

Node.js has the following modules:

  • HTTP: creates a Node.js HTTP server using classes, methods, and events.
  • Util: Provides utility functions that are useful for developers.
  • Fs: helps in dealing with I/O operations using events, classes, and methods.
  • url: provides a method for URL parsing.
  • Query string: provides a method for working with the query string.
  • Stream: provides a method to handle streaming data.
  • Zlib : helps in compressing and decompressing the files.

 Q13. Explain the purpose of module.Exports?

The module’s main purpose is to encapsulate the whole code into a single unit of code that is to be parsed by moving all the important functions into a single file.

A module can be exported with a module and can also export the function that lets it be imported to another file with a keyword.

Q14. Why is Node.js preferred over other backend technologies?

The reason why Node.js is preferred:

  • It is very fast.
  • Node Package Manager offers 50,000 bundles to the developers.
  • As Node.js never waits for an API to return the data it is perfect for real-time web applications
  • Due same code base it provides better synchronization between client and server.
  • js has a JavaScript library that makes it easy for web developers to start using Node.js in their projects.

Q15. Differentiate between Angular and Node.js?

                Angular          Node.js
It is a frontend development framework It is a server-side environment
written in TypeScript  written in languages C, C++
Used for making single-page, client-side web applications Used for making fast and scalable server-side networking applications
Divides a web application into MVC components database queries are generated

Q16. Name the data that is popularly used with Node.js?

The most common database used with Node.js is MongoDB, which is NoSQL document-oriented database.

Q17. Name the most commonly used libraries in Node.js?

There are two common libraries that are used in Node.js:

ExpressJS – It is a Node.js that is flexible with a web application framework and provides great features to develop web and mobile applications.

Mongoose – Mongoose is also a Node.js web application framework that helps in making an easy connection between an application to a database.

Q18. Tell about the pros and cons of Node.js?

Pros of Node.js:

  • It is an event-based model.
  • Uses JavaScript that is known to the developers.
  • NPM offers about 50,000 packages that give functionality to an application.
  • It is best suited when a large amount of data is to streamed and while performing I/O operations.

Cons of Node.js:

  • It is not suite when heavy computational tasks are to be performed.
  • Using call back function is complex.
  • Dealing with a relational database is difficult.
  • CPU-intensive tasks cannot be performed as Node.js is single-threaded.

Q19. Which command is used to import external files?

The “require” command is used for importing external files.

Q20. What is meant by event-driven programming?

Event-driven programming works by using events to trigger various functions like clicking a mouse button.

Q21. Define the Event loop in Node.js?

Events loops in Node.js are used to handle the call back that are asynchronous. It is also used in non-blocking input/output in Node.js.

Q22. What is the difference between process.nextTick ()and setImmediate ()?

Next Tick () is used to postpone the execution of the action until the next event loop in other words it simply calls the callback function as soon as the execution of the current loop is done whereas setImmediate executes a callback on the next cycle of the event loop and returns the control to the I/O operations.

Q23. Define EventEmitter in Node.js?

EventEmitter is defined as a class that holds all the objects that emit events.

When an object is thrown from EventEmitter Class throws an event all the attached functions to this event are called synchronously.

Q24. Name the types of API functions in Node.js?

There are two types of API functions:

  • Asynchronous, non-blocking functions.
  • Synchronous, blocking functions.

Q25. What is meant by package.json file?

The package. Json file contains the metadata for a particular project. It is found in the root directory of any node Node application or module.

Q26. How to use a URL module in Node.js?

URL module is a built-in module that splits up the web address into a readable format. It gives various utilities for URL resolution and parsing.

Q27. What is meant by Express.js Package?

Express.js package consists of features that help to develop both web and mobile applications.

Q28. How can we create a simple Express.js application?

  • The request object denotes the HTTP request and consists of properties for the request query string, parameters, body, HTTP headers, and so on.
  • The response object denotes the HTTP response which is send by an Express app sends as soon as it receives an HTTP request.

nodejs interview questions

Q29. What are the types of streams in Node.js?

There are four types of streams:

Readable – reading operations are included.

Writable − write operations are included.

Duplex −both reading and write operations are included.

Transform − A type of duplex stream where the output is computed based on input.

Q30. How can we install, update, delete a dependency?




Q31. Create a simple serve Node.js that returns Hello World?


  • Import the HTTP module.
  • Use the createServer function with a callback function using request and response as parameters.
  • Write the “hello world.”
  • Set the server to listen to port 8080 and assign an IP address.

Q32. What are asynchronous and non-blocking APIs in Node.js?

  • All Node.js library APIs are asynchronous, in other words, they are also non-blocking
  • A Node. js-based server never waits for an API to return data. Instead, it moves to the next API after calling it.

Q33. How can you implement async in Node.js?

In the below code the async code asks the JavaScript engine to wait for the request.get () function to complete before moving on to the next line for execution.


Q34. Define callback function in Node.js?

A callback function avoids any blocking and allows the other code to run in the meantime and a call back function is called after a given task.

Q35. Define REPL in Node.js?

REPL full form is Read Eval Print Loop and is similar to windows console or Linux/Unix shell in which the command is entered. Output responded by the system is :


Q36. Define the control flow function?

The control flow function is defined as a piece of code that runs between several asynchronous function calls.

Q37. How will the control flow function manage the function calls?


Q38. Differentiate between fork () and spawn () methods?

             Fork() Spawn()
Fork () is that case of spawn () that generates a new instance of a V8 engine. Spawn () releases a new set of processes with the set of commands that are available.
  On a single node codebase, multiple workers can run multiple tasks. Only a single copy of the node module is active on a processor. 

Q39. What is the use of buffer class in Node.js?

Buffer class is used to store raw data which is similar to an array of integers that corresponds to a raw memory allocation. It is used as JavaScript is not compatible with binary data.

Q40. Define piping in Node.js?

Piping is a mechanism that is used to connect the output of one stream with another. It is also used to retrieve data from one stream and pass output to another steam.

Q41. Name some of the flags used in the read/write operations in files?


Q42. How to open a file in Node.js?

The syntax to open a file in Node.js is, flag[,mode],callback)

Q43. Define callback hell?

Callback hell also called the pyramid of doom, is due to the intensively nested, unreadable, and unmanageable callbacks, that in turn make the code harder to read and debug. In simple words, uneven implementation of the asynchronous logic causes callback hell.

Q44. What is meant by reactor pattern in Node.js?

The reactor pattern is based on non-blocking I/O operations. when the I/O request is generated then it provides a handler which then submit it to the demultiplexer.

Q45. What is meant by the test pyramid in Node.js?

Below image describes test Pyramid:


Q46. Why does Google use the V8 engine for Node.js?

V8 converts JavaScript code into machine code in order to increase performance. During execution, it turns JavaScript code into machine code by using a JIT (Just-In-Time) compiler, as do many current JavaScript engines such as SpiderMonkey or Rhino (Mozilla).

Q47. What are Node.js exit codes?


Q48. What is the concept of middleware in Node.js?

Middleware is a function whose sole purpose is to receive and respond to objects. Tasks performed by the middleware are:

  • Executing any code.
  • Updating the request and response of the object.
  • Executes the request and response cycle.

Q49. List different types of HTTP requests?

HTTP requests are a set of requests that are used to perform certain actions.

  • GET: retrieving the data.
  • POST: used to make a change in state or reactions on the server.
  • HEAD: Similar to the GET method, the only difference is it asks for the response without the response body.
  • DELETE:deletes the predetermined resources.

Q50. How is MongoDB database to Node.js?

To create a database in MongoDB:

  • Firstly, create a MongoClient Object.
  • Mention a URL with correct details of IP address and name of the database you desire to create.

 Q51. What is the aim of NODE_ENV?


Q52. Mention the various features of Node.js timing?



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